I just went through cleanng up and repainting the black on the original wheels and the "rubber/plastic" cap does a poor job if not non existant job of centering the wheel on the boss which peers through the drum brake. I'm finding that the best way to get the wheel centered as best I can is to get each pair of lug nuts that are across from each other to spin freely while the other two hold the wheel firmly in place. Then I get an average in centering the wheel. This is certainly as awful as a Land Rover but at least there is symetry with four lugs. I'll measure the boss on the axel tonight as the caliper is in hand. I might have to make some sleeves that do this properly and just let the lugs draw the wheel down the way they are intended too!